The biological response of tumors to photodynamic
therapy (PDT) is complex and involves a combination of cell kill, vascular
damage, and induction of immune/inflammatory responses, all of which result
in varying changes in contrast on MR images. In this study, we examined the
utility of MRI in monitoring tissue response to PDT in an invasive,
intramuscular model of squamous cell carcinoma. Our results demonstrate the
potential value of MRI as a tool to monitor PDT-induced tissue damage in
vivo.